Once before in his lifetime, an invasion of his eastern provinces had required his immediate presence, and allowed his adversary to quit Mesopotamia and march against Magnentius.

It is not improbable that a fresh attack of the same or some other barbarians now again happened opportunely for the Romans, calling Sapor away, and thus enabling Constantius to turn his hack upon the East, and set out for Europe in order to meet Julian.
The meeting, however, was not destined to take place.

On his way from Antioch to Constantinople the unfortunate Constantius, anxious and perhaps over-fatigued, fell sick at Mopsucrene, in Cilicia, and died there, after a short illness, towards the close of A.D.361.

Julian the Apostate succeeded peacefully to the empire whereto he was about to assert his right by force of arms; and Sapor found that the war which he had provoked with Rome, in reliance upon his adversary's weakness and incapacity, had to be carried on with a prince of far greater natural powers and of much superior military training..